Method of producing a sewer pipe

ABSTRACT

THIS INVENTION DEALS WITH A METHOD OF CONTINUOUSLY FORMING A SEWER PIPE WITHIN A DITCH. THE METHOD COMPRISES THE FORMATION OF PLASTIC SHEETS TO CONFORM TO THE INNER CROSS-SECTIONAL CONFIGURATION OF THE PIPE, MOVING THE APPARATUS ALONG THE BOTTOM OF THE DITCH WHILE FEEDING THE SHEETS TRHOUGH THE APPARATUS INTO THE DITCH AND INTERCONNECTING SAID SHEETS. CONCRETE IS THEN POURED INTO THE DITCH ONTO THE SUCCESSIVELY CONNECTED SHEETS TO FORM THE PIPE WHILE THE APPARATUS IS VIBRATED.

Feb. 9, 1971 w Q OLSON 3,562,056

METHOD OF PRODUCING A SEWER PIPE Original Filed Jan. 27. 1966 2 Sheets-Sheet 1 4 j @fw/m.

Feb. 9, 1971 w, Q OLSON 3,562,056

METHOD OF PRODUCING A SEWER PIPE Original Filed Jan. 27. 1966 2 Sheets-Shoot 2 Tranc Z5164 #WWJ 7 United States Patent 3,562,056 METHOD OF PRODUCING A SEWER PIPE William C. Olson, West Sacramento, Calif., assignor to Thunder Enterprises, Inc., West Sacramento, Calif., a corporation of California Original application Jan. 27, 1966, Ser. No. 523,418, now Patent No. 3,470,918, dated Oct. 7, 1969. Divided and this application Apr. 25, 1969, Ser. No. 840,885

Int. Cl. B28b 1/08; E04b 1/16 US. Cl. 156-293 9 Claims ABSTRACT OF THE DISCLOSURE This invention deals with a method of continuously forming a sewer pipe within a ditch. The method comprises the formation of plastic sheets to conform to the inner cross-sectional configuration of the pipe, moving the apparatus along the bottom of the ditch while feeding the sheets through the apparatus into the ditch and interconnecting said sheets. Concrete is then poured into the ditch onto the successively connected sheets to form the pipe while the apparatus is vibrated.

This application is a division of SN. 523,418, now Pat. No. 3,470,918.

This invention relates to a sewer pipe and, more particularly, relates to a concrete sewer pipe having an acidresistant plastic liner.

It is well known that concrete deteriorates when subjected to the corrosive fumes of sewage largely because the fumes includes sulfuric acid but a concrete sewer pipe is practical if it is lined with a suitable impermeable inert material such as a suitable acid-resistant plastic. It is also known, as set forth in the Edward Pat. 2,243,273, that since it is primarily the fumes and not the liquid sewage that attacks the concrete, the inert liner need extend no lower than the minimum liquid level in the sewer line.

All of the prior art procedures within my knowledge for fabricating such a composite sewer pipe, however, are not continuous fabrication procedures and therefore are not economical in comparison to well known methods of continuously forming a concrete water pipe in a single operation. A continuous method of fabricating an unlined concrete pipe is set forth, for example, in the two Tunsen Pats. 2,731,698 and 3,106,760, which prior art disclosures are hereby incorporated into the present disclosure by reference.

In the Tunsen fabrication procedure, a ditch is dug and an apparatus is placed in the ditch for progressive movement along the ditch by means of a cable and winch mechanism. The apparatus has a hollow arcuate mandrel shaped in accord with the desired inner circumference of the concrete pipe and has an upper wall spaced above the the mandrel to shape the outer top surface of the concrete pipe. -In addition, the moving apparatus has a hopper to receive concrete for forming the concrete pipe and has suitable means to vibrate the apparatus to cause the concrete to settle and become compact. As the apparatus moves along the ditch, successive metal form sheets are added by introduction over the hollow mandrel and concrete from the hopper flows over and around the successively added form sheets. A single vibrator may be located on the above mentioned upper wall of the apparatus or on the hopper or a plurality of vibrators may be provided at spaced points on the apparatus.

The metal form sheets are interconnected end to end to form a continuous series with the initial end of the series anchored to keep the series stationary .as the apparatus moves along the ditch. As the successive arcuate metal form sheets emerge from the apparatus, suitable transverse struts are placed inside the sheets to reinforce the sheets against the weight of the newly poured concrete and after the concrete sets both the struts and the metal form sheets are withdrawn from the interior of the concrete pipe.

To make it possible to remove the metal form sheets readily from the cured concrete each sheet is of less circumferential extent than the inner circumference of the concrete pipe so that the sheet may be readily contracted by flexure to a diameter less than the inside diameter of the finished concrete pipe. Since the concrete tends to adhere tenaciously to the metal form sheets and the adherence is increased by the vibration that compacts the concrete, the vibration must be kept moderate to avoid making it too diflicult to dislodge the metal form sheets.

With reference to the present invention, wherein suitable acid-resistant plastic sheet material permanently lines a concrete sewer pipe it would be advantageous to have the concrete adhere tenaciously to the liner, but unfortunately concrete does not tend to adhere to the plastic sheet and therefore the liner cannot be held in place by adhesion of the concrete. This problem of keeping the liner snugly in place has been solved by using curved plastic sheets of less circumferential extent than the inner circumference of the concrete pipe, with two lower longitudinal edge portions of the sheets spaced apart to expose the concrete below the anticipated minimum level of the liquid sewage. Adequate anchorage of the liner sheet is accomplished simply by bending the lower longitudinal edge portions of the sheet to diverge outwardly from the inner circumference of the concrete pipe so that the longitudinal edge portions of the sheet become embedded in the concrete for permanent anchorage of the liner sheet. The invention takes advantage of the well known fact that concrete contracts as it cures, the shrinking of the concrete resulting in snug contact between the concrete and the liner sheet.

To carry out the new procedure for continuous fabrication of a concrete sewer pipe,'an apparatus is used that is constructed in the general manner disclosed in the two Tunsen patents and the liner sheets are successively introduced and interconnected in the same general manner as the temporary metal form sheets in the prior art procedure. The vibratory means of the apparatus may be operated at as high an energy level as may be desirable for thoroughly compacting the cement.

An important feature of the invention is that the vibration of the apparatus is transmitted to the plastic liner sheets and thereby serves two new purposes. One of the new purposes is to drive the divergent lower longitudinal edge portions of the plastic sheets into the newly poured concrete that forms the pipe. The other of the new purposes of the vibratory means is to cause the local formation of slurry in the concrete to envelope and seal the lower divergent longitudinal edge portions of the plastic sheets.

Arcuate struts are employed temporarily inside the newly formed sewer pipe to reinforce the liner sheets against the weight of the concrete until the concrete cures. One feature of the invention is the use of reinforcing struts of such shape as to tend to spread the liner sheets and thus tend to drive the divergent lower edges of the sheets into the concrete. An important unexpected advantage of the use of the temporary reinforcement struts is that the struts provide downward diagonal paths along which the vibratory forces are transmitted and directed against the inner surfaces of the liner sheets to result in the application of a desirably high level of vibratory energy at the lower longitudinal edges of the sheets.

A further feature of the invention is the concept of encouraging penetration of the divergent lower edge portions of the liner sheets into the concrete by employing sheet material that has plastic memory and by initially forming the liner sheets to a somewhat larger radius of curvature than the planned inside radius of the concrete pipe. The tendency of the plastic liner sheet to expand in diameter is concentrated at the lower free divergent edges of the sheets.

The various features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a diagrammatic longitudinal sectional view of an apparatus of the character described moving along the bottom of a ditch in the process of continuously forming a lined sewer pipe;

FIG. 2 is a fragmentary perspective view showing how the liner sheets are interconnected end for end in a linear series;

FIG. 3 is a fragmentary sectional view taken along the line 33 of FIG. 2 showing how two successive plastic sheets in the series interlock with each other;

FIG. 4 is an enlarged sectional view showing how acidresistant adhesive material is placed in a groove in one sheet prior to the mechanical interlocking of the two sheets;

FIG. 5 is a side elevation of a temporary reinforcement strut that may be used in the practice of the invention;

FIG. 6 is a sectional view showing the cross-sectional configuration of a trench in which the lined concrete sewer pipe is to be formed;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 1 showing the initial flow of concrete from the hopper over an arcuate plastic liner sheet;

FIG. 8 is a similar view at a more advanced stage of the flow of the concrete;

FIG. 9 is a similar view showing the finished pipe in cross section and showing a reinforcement strut being dislodged for removal; and

FIG. 10 is a cross-sectional view of a finished sewer pipe in actual service.

The invention employs a plurality of arcuate plastic liner sheets 10 of the character shown in FIGS. 2 and 3. Each liner sheet 10 is made of a suitable acid-resistant plastic and for this purpose may be made of an isophthalic base polyester resin, for example a Chevron Type 5893 polyester resin manufactured by the California Chemical Co. Each of the liner sheets is perfectly reinforced by embedded glass fibers and is formed to a radius of curvature that is slightly larger than the desired radius of curvature of the inside of the sewer pipe.

The circumferential extent of each of the liner sheets 10 is substantially less than the inner circumference of 0 the sewer pipe because the liner is not intended to cover the bottom inner surface of the concrete pipe below the minimum level of the liquid sewage. Since it is intended that the two spaced lower longitudinal edge portions 12 of the liner sheet will be embedded in the concrete wall of the pipe, these longitudinal edge portions are bent outward to diverge from the curvature to which the sheet is formed.

It is essential that the arcuate liner sheets 10 be adapted for interconnection in end to end relationship to form a continuous series that is capable of withstanding a mod erate amount of stress in tension. For this purpose it is contemplated that the sheets will be formed with shoulders, preferably hooked-shaped shoulders, to interlock in a positive manner.

In the present embodiment of the invention, one end of each sheet is formed with a radially inwardly oifset portion 14 as shown in FIG. 4 and this offset portion is formed with a circumferentially extending groove 15 that is undercut to form a hook-shaped shoulder 16. The other end of the arcuate liner sheet is formed with a radially outwardly protruding rib 18 that is undercut to form a hook-shaped shoulder 20 shaped and dimensioned to make positive engagement with the hook-shaped shoulder 16 of an adjacent arcuate liner sheet.

Since the juncture between two of the acid-resistant liner sheets 10 must be fluid tight and acid resistant, a suitable acid-resistant adhesive 22 is deposited in the groove 15 as shown in FIG. 4 prior to the insertion of the rib 18 of an adjacent sheet into the groove. The adhesive may be, for example, a polyurethane adhesive, or other acid resistant adhesive. It is to be noted that the gr ove 15 is substantially Wider than the rib of the complemen tary rib 18 to provide a desirable degree of freedom for relative movement of the rib in the groove so that two consecutive interlocked liner sheets may be at an angle relative to each other to make it possible for the concrete pipe to curve to gradually change direction wherever such a change in direction is desired.

The apparatus for continuously forming the pipe is of the character disclosed in the previously mentioned Tunsen patents and is shown diagrammatically in FIG. 1. The apparatus is dimentioned to fit into a ditch of the crosssectional configuration shown in FIG. 6, the apparatus having a rounded bottom wall 24, two opposite side walls 26 for sliding contact with the side walls of the ditch and a roof 26 interconnecting the two side walls. The roof and side walls form a work space 28 forward of a rigid arcuate hollow mandrel 30 having an outside diameter equal to the desired inside diameter of the finished sewer. A lower portion 32 of the mandrel projects rearward to function as a trowel for shaping the floor of the sewer and an upper arcuate wall 34 above the mandrel serves as a trowel to shape the upper outer surface of the concrete pipe. A suitable upright hopper 35 feed-s concrete to the successive plastic liner sheets on the mandrel as the apparatus moves forward or to the right as viewed in FIG. 1. The apparatus is moved slowly forward by means of a cable 36, one end of which is anchored in the ditch and the other end of which is wound onto a power actuated winch (not shown) inside the apparatus- To start the continuous fabrication of a length of the sewer pipe, an arcuate liner sheet 10 that is to start the series of interconnected liner sheets is suitably anchored in the ditch so that the chain of liner sheets will remain stationary and not be dragged forward by frictional contact with the moving apparatus. FIG. 1 shows an interconnected series of liner sheets Illa-10f extending from a remote point of anchorage to and over the mandrel 30. A workman in the work space 28 has just attached a new arcuate liner sheet 10g to the end of the series. In making this connection the workman applies adhesive 22 to a groove 15 on the rear end of the sheet 10 in the manner shown in FIG. 4 and then adds the liner sheet 10g to the series by pressing the rib 18 of the new liner sheet into the groove for hook engagement with the hook-shaped shoulder 16 of the liner sheet 10 With the apparatus moving slowly to the right in FIG. 1, successive arcuate liner sheets 10 are added in the manner described with the hopper 35 depositing concrete on the newly added liner sheets as the liner sheets slide on the surface of the mandrel 30. The newly added concrete flows downward on the opposite sides cf the arcuate liner sheets as shown in FIGS. 7 and 8 with the two streams of concrete meeting to complete the configuration of the pipe as shown in FIG. 9. As the arcuate upper wall 34 shapes the top surface of the continuously formed concrete pipe, the apparatus is vibrated in a manner to facilitate flow of the concerete and to cause the concrete to take a compact form without any voids. Any number of vibrators may be mounted on the apparatus for this purpose. FIG. 1 shows a vibrator 38 actuated by a motor 40, the vibrator being mounted on the upper wall 34 to direct pulsating force downward through the newly poured concrete.

As the hollow mandrel 30 of the rightwardly moving apparatus clears the successive liner sheets 10 to expose the inner surfaces of the liner sheets, a workman inside the mandrel at its trailing end mounts temporary reinforcement struts 42 inside the liner sheets to brace the liner sheets against the weight of the concrete. The struts 42 may be positioned at any points along the liner sheets. As shown in FIG. 1 the struts 42 may be positioned advantageously at the junctures of the successive liner sheets.

After the concrete sets, a workman enters the finished sewer pipe to remove the struts 42. FIG. 9 shows how a strut 42 may be dislodged and turned for removal from the sewer pipe.

In the preferred practice of the invention each of the struts 42 is of the configuration shown in FIG. 5. The strut may be made of various materials including metal, plywood and plastics. As shown in FIG. 5, the strut is of open construction for lightness and ease of handling. The strut 42 has an upper arcuate edge 44 of the configuration of a half circle of the same radius as the inner circumference of the sewer pipe and the strut further has two opposite downwardly extending side edges which diverge outwardly from the curvature of the arcuate edge 44. In this instance the two side edges 45 are tangential to the arcuate edge 44 and are substantially vertical when the strut is positioned inside a liner sheet. It is apparent that since the side edges 45 diverge outwardly from the curvature of the upper arcuate edge 44, the two side edges have a spreading effect on the two legs of the liner sheet and thus tend to drive the outwardly bent lower edge portions 12 of the liner sheet into the concrete as may be seen in FIG. 8.

The vibration of the apparatus is transmitted to the regions of the two lower edge portions 12 of the liner sheet along various paths. Thus with the vibrator 38 mounted on the upper wall 34, pulsations or waves of energy are directed downward along the paths of flow of the concrete as indicated by the outer arrows in FIGS. 7 and 8. The pulsating energy is also directed against each of the newly installed struts 42 to follow diagonal paths through the struts as indicated by the wavy arrows in FIGS. 7 and 8.

In is important to note that since the maximum pressure of a newly installed strut 42 against the surrounding liner sheet is in the region of the two opposite lower corners of the strut where the strut spreads the liner, the vibratory forces are transmitted effectively to the lower corners to promote pulsation of the two opposite legs of a liner sheet. In addition, it is to be noted that the rearwardly extending lower portion 32 of the mandrel is a rigid part of the apparatus and therefore is vibrated along with the upper wall 34. The vibrations of the extension 32 are directed towards the two lower edge portions 12 of a liner sheet and has substantial effect because the lower portion of the mandrel is quite close to the lower edge portions 12 of the sheet as may be seen in FIG. 8.

It has been found that the vibration of the liner sheets drives their outwardly bent lower portions 12 into the concrete and it has been further found that the vibrating edge portions caused pools of slurry to develop. The pools of slurry are exceptionally rich in cement and result in the edge portions 12 of the sheets being effectively sealed in the concrete.

As heretofore stated the concrete shrinks slightly when it cures with the result that the concrete of the finished pipe fits snugly over the plastic liner and desirably places the plastic liner under a certain degree of circumferential compression. As heretofore stated it is contemplated that the two lower edges of the plastic liner will be below the liquid level when the sewer is placed in service. It has been found, however, that if the liquid level does fall somewhat below the liner to expose some of the concrete to the fumes of the sewage, no significant deterioration of the concrete occurs because the fumes tend to accumulate in the upper portion of the sewer pipe.

My description herein of the selected practice of the invention in specific detail will suggest various changes, modifications and other departures from my disclosure within the spirit and scope of the appended claims.

I claim:

1. A method of continuously forming a sewer pipe in a ditch, characterized by the use of an apparatus that is movable through the ditch longitudinally thereof, said method including the steps of:

forming sheets of acid resistant plastic material to conform to the inner cross-sectional configuration of the sewer pipe with the circumferential extent of each sheet less than the inner circumference of the sewer pipe to line the upper and side surfaces of the interior of the sewer pipe with two lower longitudinal edge portions of the sheet spaced apart and bent outward from the curvature of the sheet;

moving the apparatus progressively along the bottom of the ditch,

feeding said sheets in succession through the apparatus into the ditch and interconnecting the successive sheets to form a series of sheets connected together end for end;

anchoring the series of sheets against movement longitudinally of the ditch;

pouring concrete into the ditch onto the successively connected sheets to form a hollow concrete body lined by the series of sheets with said lower longitudinal edge portions of the sheets embedded in the concrete of the hollow body and leaving the bottom portion of the inner surface of the hollow body exposed to the interior of the hollow body; and vibrating the apparatus to convey vibration to the sheets to drive the spaced lower longitudinal edge portions of the successive sheets into the concrete and to create slurry locally in the concrete to seal the lower edge portions of the sheets in the concrete.

2. A method as set forth in claim 1 which includes the further step of temporarily mounting a series of reinforcement struts in the series of sheets to withstand the weight of the concrete until the concrete cures and in which the upper edge of each of the reinforcement struts conforms substantially to a semicircle of the curvature of said mandrel of the apparatus and the two lower side edges of the strut diverge outwardly from the curvature of the upper edge to spread the lower edge portions of the sheets apart to encourage penetration of the concrete by the lower edge portions.

3. A method as set forth in claim 2 which includes the step of vibrating the apparatus to convey vibrant energy through the reinforcement struts to sheets in the regions of the lower corners of the struts.

4. A method of continuously forming a sewer pipe in a ditch, characterized by the use of an apparatus that is movable through the ditch longitudinally thereof, the apparatus having a mandrel to shape the interior of the sewer pipe, said method including the steps of:

forming sheets of acid resistant plastic material to conform to the inner cross sectitonal configuration of the sewer pipe with the circumferential extent of each sheet less than the inner circumference of the sewer pipe to line the upper and side surfaces of the interior of the sewer pipe with two lower longitudinal edge portions of the sheet spaced apart and diverging outward from the curvature of the sheet;

moving the apparatus progressively along the bottom of the ditch;

feeding said sheets in succession over said mandrel of the apparatus into the ditch and interconnecting the successive sheets to form a series of sheets connected together end for end;

anchoring the series of sheets against movement longitudinally of the ditch;

pouring concrete into the ditch at the moving apparatus onto the successive sheets on the mandrel to form a hollow concrete body lined by the series of sheets; and

vibrating the apparatus to compact the concrete and to drive the spaced lower longitudinal edge portions of the successive sheets into the concrete and to create slurry locally in the concrete to seal the lower edge portions of the sheets in the concrete.

5. A method as set forth in claim 4 which includes the step of temporarily mounting support means inside the series of sheets to reinforce the series of sheets while the concrete cures.

6. A method as set forth in claim 5 which includes the step of installing reinforcement struts inside the sheets to reinforce the sheets, the reinforcement struts being installed close enough to the apparatus to transmit vibrations from the apparatus to points at relatively low level on the inner surface of the sheets.

7. A method of continuously forming a sewer pipe in a ditch, characterized by the use of apparatus that is movable through the ditch, the apparatus having a mandrel of the desired radius of curvature of the interior of the sewer pipe to shape the interior of the sewer pipe, said method including the steps of:

forming sheets of acid resistant plastic material to conform to said radius of curvature,

each of said sheets having a circumferential extent substantially less than the inner circumference of the sewer pipe whereby the two lower longitudinal edge portions of each sheet are spaced apart;

bending each of the lower longitudinal edge portions of each sheet outward from said radius of curvature;

moving the apparatus progressively along the bottom of the ditch;

feeding said sheets in succession over said mandrel of the apparatus into the ditch and interconnecting the successive sheets to form a series of sheets connected together end for end;

anchoring the series of sheets against movement longitudinally of the ditch;

pouring concrete into the ditch at the moving apparatus onto the successive sheets to form a hollow concrete body lined by the series of sheets;

a 8 vibrating the apparatus to compact the concrete and to drive the spaced lower longitudinal edge portions of the successive sheets into the concrete and to create slurry locally in the concrete to seal the lower edge portions of the sheets in the concrete. 8. A method as set forth in claim 7 in which the sheets are formed to a radius of curvature larger than said desired radius of curvature thereby to bias the two longitudinal edge portions of each sheet outward away from each other to encourage penetration of the longitudinal edge portions into the concrete.

9. A method as set forth in claim 7 which includes the steps of:

forming transverse grooves in one of the leading and trailing ends of the sheet on one face of the sheet;

forming a transverse rib on the opposite face of the sheet on the other of said leading and trailing ends of the sheet;

depositing acid resistant adhesive material in the grooves of the successive sheets; and

inserting the transverse ribs of successive sheets into the transverse grooves of successive sheets to interconnect the sheets with acid resisting fluid tight joints.

References Cited UNITED STATES PATENTS 1/1919 Carr 2532 9/1965 Martin 2532 US. Cl. X.R. 264-32, 33, 35, 

